1. Technical Field
The present invention relates to a projection zoom lens system of a projector apparatus that enlarges and projects an image using a light valve, onto a screen.
2. Description of the Related Art
Conventionally, a liquid crystal panel is often used as the light valve of a projector. In recent years, in place of a liquid crystal panel, apparatuses equipped with a plurality of elements and forms an image by mechanically changing the direction of reflection of light using a micromachining technique have been realized. One example of such an apparatus is a DMD (digital mirror device or display) in which minute mirror-surface elements (micromirrors) are arranged in an array corresponding to pixels and image is formed by controlling the angles of the respective mirror surfaces. Compared to a liquid crystal panel, a light modulator (light valve) in which pixels are composed of micromirrors has faster response and produces a brighter image, so that such light modulator is suited to the realization of a compact projector with high luminance and high image quality.
In a DMD, the micromirrors rotate for making an image around ±12 degrees, so that illuminating light (source light) provided from an illumination optical system (light source system) is converted into effective or active reflected light (modulated light or projection light) that is active for forming an image and non-effective or inactive reflected light that is not active for forming the image. Accordingly, a projector that uses a DMD as a light valve requires a projection lens or lens system that catches (takes in) the active reflected light (referred to as “active light” or “projection light”) and does not catch (does not take in) the inactive reflected light (referred to as “inactive light”). In addition, in order to reduce the image circle, the projection lens should be preferably set in the direction of a normal for the DMD. Accordingly, limitations are placed on the arrangement of the illumination optical system that inputs illuminating light into the DMD and the projection lens system that outputs the projection light. Namely, in order to input the active light from the DMD into the projector lens as described above, it is necessary to dispose the illumination optical system and the projection lens system in approximately the same direction.
There are also demands to make projector apparatuses that use a DMD smaller or more slimline. The use of compact lenses with small diameters as the projector lens is being studied. A projection lens system comprising a convex lens (a field lens) placed on the front side of the light valve, which is the light modulating apparatus, is studying for simplifying and compacting the lens system. In this lens system, the convex lens that places on the front side of light valve is used as part of both the illumination optical system and the projection lens system for simplifying the illumination optical system, and aberration correcting of the projection lens system.
A projector zoom lens system including the field lens placed in front of the light valve for using in both the illumination optical system and the projection optical system should be suited to a projector. However, suitable, practical or usable configuration of such lens system has not been disclosed yet. It is therefore an object of the present invention to provide a favorable projection zoom lens for a projector that uses such a field lens. It is a further object to provide a projector apparatus that is compact but is equipped with a zoom function.